The invention relates generally to the field of liquid crystal displays (LCDs). More particularly, the invention concerns a liquid crystal display element, a liquid crystal display and method of making same in which a select one of two bonded substrate components has a plurality of vias filled with an optical grade adhesive in a manner to eliminate voids in the vias thereby, substantially eliminating light scattering during LCD operations.
Conventional liquid crystal displays are formed by bonding two substantially planar substrates, commonly referred to as a panel electrode, and a drive or signal substrate, together with a gap between them and then injecting a liquid crystal in the gap. Electrical connectivity between the drive and panel substrates is typically achieved with an anisotropic conductive film that connects wiring terminals on a flexible polyimide drive substrate with transparent electrode terminals formed on the panel substrate. Prior to bonding the substrates, a transparent coating of indium tin oxide (ITO) is deposited on both the panel and drive substrates forming a patterned ITO layer on the substrate(s). After forming the patterned ITO layer, the two glass substrates are then bonded together with a known gap therebetween. To complete the manufacturing process of the LCD, a liquid crystal material is then vacuum filled in the gap of the bonded substrates thereby forming an active liquid crystal display.
U.S. Pat. No 5,629,787, entitled xe2x80x9cMethod For Producing An LCD By Pressing The Substratesxe2x80x9d by Tsubota et al., May 13, 1997, is illustrative of an existing process for making a typical liquid crystal display in which a spacer is used to determine the gap between the transparent substrates. Moreover, an ITO layer is coated only on one active surface of the transparent substrate. This reference, however, does not teach the presence of a plurality of adhesive filled, void-free vias formed in one of the substrates.
Canadian Patent Application No. 2,279,780, entitled xe2x80x9cLight Density Control With LCD Arrangementxe2x80x9d by Kraft, et al. filed Aug. 9, 1999, discloses a LCD arrangement with improved exposure control in a photo finishing environment in which multiple picture elements (pixels) associated with electrodes are positioned on bonded transparent plates and feed conductors to the electrodes feed control signals thereto. Referring to FIG. 1, a typical prior art LCD display element 1 contains vias 2 or feed throughs in a transparent substrate 3 and patterning of an ITO layer 6 on opposed active surfaces 4 and 5. Although the reference teaches vias 2 filled with an adhesive material layer 9 in the transparent substrate 3, the reference clearly recognizes that air bubbles or voids 8 exist in the adhesive material 9 filling the vias 2 that necessitates vacuum removal. Moreover, the reference does not recognize controlling the height and thickness of the adhesive material 9 as important factors in bonding a deck plate 7 to a transparent substrate 3 with an ITO coating layer 6 applied to the active surfaces 4, 5 or filling the vias 2.
U.S. Pat. No. 6,061,105, entitled xe2x80x9cLCD With Via Connections Connecting The Data Line To A Conducting Line Both Before And Beyond The Sealing Materialxe2x80x9d by Nakagawa, May 9, 2000, discloses a liquid crystal display device that can eliminate an electrostatic discharge (ESD) problem resulting from a high dielectric constant filler that is appropriate for improved shape stability of a sealing material. While this reference is generally believed to teach a good solution to the electrostatic discharge problems encountered in the LCD display fabrication process, it does not teach or suggest adhesive filled, void-free vias formed in one of the substrates.
U.S. Pat. No. 6,061,105 discloses using vias connections in thin film transistors (TFT) connections. This reference, however, does not present vias in the transparent substrate that feed ITO from one active surface to an opposed active surface of the transparent substrate. According to the prior art reference, the vias are formed in the seal area and outside the active pixels area of the display. Thus, the reference does not contemplate the use of optical grade adhesives nor the need to maintain transparency in the active area. Hence this reference shows no appreciation for Applicants"" problem or proposed solution.
Therefore, a need persists in the art for a liquid crystal display element and method of making same in which vias are formed in a substrate and then specially filled with an optical grade adhesive. The adhesive material filling the vias are virtually free of voids which substantially eliminates light scatter in an operating LCD, for instance, in a photofinishing application.
It is, therefore, an object of the invention to provide a method of constructing a liquid crystal display (LCD) element having vias formed in one of two transparent substrates filled with an optical grade adhesive material in a manner that resists the scatter of light.
Another object of the invention is to provide such a method in which the vias in the aforementioned LCD element are filled in a manner to substantially eliminate the presence of voids in the optical grade adhesive materials filling the vias.
The present invention is directed to overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the present invention, a method of constructing a liquid crystal display includes providing a first transparent substrate having a first surface and an opposed second surface. A first ultra-violet protective coating is deposited on the first surface. Further, a second transparent substrate is provided for fixedly attaching to the first transparent substrate with a predetermined gap therebetween. Second transparent substrate has a first active surface for bonding with the second surface of the first transparent substrate. Unique to our invention, second substrate also has a second active surface opposite the first active surface and a plurality of vias passing between the first active surface and the second active surface to facilitate electrical continuity between said first active surface and said second active surface. An optical grade adhesive material is controllably dispensed in the gap between the first transparent substrate and the second transparent substrate so as to fill each one of the plurality of vias in the second transparent substrate to a predetermined plug height. The adhesive material is cured so as to bond the first and second transparent substrates to form a LCD element. Using conventional LCD manufacturing processes, an electrode panel is fixedly attached to the LCD element having a signal plate and deck plate. Once the LCD is formed, a liquid crystal material is dispensed in the gap between the electrode and the LCD element for energizing the liquid crystal display.
Thus, the method of the present invention has numerous advantageous effects over prior art developments, including: air bubble free or void-free adhesive material filling vias formed in the signal plate, air bubble free or void free adhesive material bonding the signal plate and deck plate; thickness controlled adhesive material levels dispensed into vias, efficient vias fill associated with controlled signal to deck plate gap width, fewer process steps in the LCD subassembly process, and, substantially simple process for locating the deck plate in the LCD element.